For a 12×12 room I would say the minimum would be 4 RGB cans, if you can invest in 8 that would be very nice. For 12×12 even one Revo can do well if placed right as it has a huge angle of display.
As for fog or haze… I like fog as I like to control when I fog it up and sometimes you need to let the fog go, because people react badly to it.
The problem with fog machines is that the cheap ones will also make cheap looking fog. So the minimum I would recommend is something like the ADJ Fog Storm 1200.
Haze I only use for band stuff, where you have a podium or stage that can do with some haze and that flows nicely. A simple ADJ Haze generator will do, as it is heaterless it is instant haze for a song if need be.